My customers usually don't look at the code I wrote, only at the pixels on the screen. Some of them even make me use their repositories but I think that in the last few years there was only one quick code review, after a customer got bought by another company. Nevertheless I keep writing tests and all the right stuff because they make my job easier.
During my years as freelancer I also rarely had a client look at the code although they had access to it. But I can imagine with some tech-savvy customers there is a lot of value in using Github.
